1. Field of the Invention
This invention relates generally to digital temperature control systems, and more particularly a digital temperature control system employed in an air-conditioner or refrigerator which needs strict temperature control.
2. Description of the Prior Art
Heretofore, many types and methods of temperature control systems have been in use for air-conditioners and refrigerators.
These preceding temperature control systems were of the analog type operated with analog signals.
A typically conventional analog type temperature control system employs a thermister for detecting temperature and a variable resistor for adjusting the desired temperature.
An analog amplifier is also used to amplify the difference in the electric resistances of both the thermistor and the variable register in order to generate a greater control signal, and the machine, as a result, functions to decrease the difference between the present temperature and the desired temperature.
In accordance with the performance of the machine the room temperature gradually decreases until it reaches the predetermined level. The temperature undergoes fluctuations within the preset range. This conventional analog type temperature control system, however, depends to a large extent on the qualities of the elements, particularly on the quality of the variable resistor.
The variable resistor naturally deteriorates and wears out with increasing uses of the machine. In addition, there are initial deviations in its quality, thus making it impossible to correctly control the room temperature.
The degradation of the variable resistor often brings about unstable operation and a resultant malfunctioning of the machine.